1. Field of the Invention
This invention relates to a method and apparatus for interfacing a data processing device to a host system, and more particularly to a method and apparatus for interfacing a data processing device to a host system and capable of infallibly notifying the host system of statuses of the data processing device.
2. Discussion of the Background
Conventionally, computer peripheral devices such as printers, scanners, and so on have been provided with a power control system in which the power to the machine is turned on and off when a host system such as a personal computer is turned on and off. However, there has is recently been developed another type of computer peripheral device that includes a facsimile function and therefore requires power at all times regardless of whether the host system is turned on. One such type of computer peripheral device is referred to as a multiple function peripheral (MFP), capable of performing a variety of functions such as printing, scanning, copying, and facsimile in one unit. Such an MFP generally has a data transmitting function for transmitting data to the host system and a data receiving function for receiving data from the host system.
Because of environmental conservation concerns, many institutes for industrial standards in various countries have recently been issuing recommendations for reducing power consumption of data processing apparatuses, including computer peripheral devices, when in a machine idling mode. However, reduction of power consumption in a machine idling mode has raised technical issues regarding connected systems. That is, two separate systems connected through an interface device are required to be capable of detecting a request for action from each other and, at the same time, reducing power consumption when in a machine idling mode.
Japanese Laid-Open Patent Publication No. JPAP08-224944 (1996) has introduced a printer which addresses this technical issue. This printer is provided with a power shut-down circuit which can automatically turn off power by judging the power status of a host system by reading the voltage level of a strobe signal from the host system.
In addition to the host system and the computer peripheral devices, interface devices which interface between the host system and the computer peripheral devices are preferably turned off during the machine idling mode since these interface devices generally demand a relatively high circuit-drive capability and therefore consume a relatively large amount of power. Accordingly, techniques have been studied for reducing power consumption in an interfacing device by dropping all the receiver power other than the power necessary for performing an access detection during a machine idling mode.
Although the present invention is not limited to an MFP having an interface to a host system, the following description describes an MFP as one example. Generally, an interface device between a host system and an MFP is conformable to a parallel interface such as Centronics standard interface using a Centronics connector. This interface device includes a plurality of command signal lines from the host system, a plurality of status signal lines from the MFP, and a plurality of bidirectional data lines. In the interface device, receiver terminal side lines are usually pulled up to a power line.
Such a parallel interface is generally designed in accordance with one or more of the circuits as shown in FIGS. 8A-8D or an equivalent. The circuits include drivers as output circuits, on a driver side 41 of a cable 40 and receivers as receiving circuits on receiver side 42 of the cable 40. FIG. 8A shows input and output buffers 32 and 30, respectively, each provided with a protection diode 34 provided between a power line PL and power input of the buffer. Parasitic diodes 36 are provided between protection diodes 34 and the output or input lines to buffers 30, 32 respectively and between the output and input lines and ground, as shown. In this case, protection diodes 34 are provided to protect the power supply of a powering device from flowing into a powered-down device through the parasitic diodes 36. FIG. 8B shows input and output buffers 32, 30, respectively, configured to eliminate the need for several of the parasitic diodes 36 but which includes a protection diode 34 for inhibiting a voltage leakage through a common pull-up resistor Rp on the receiver side 42. FIG. 8C shows an open-drain driver which includes a pull-up resistor Rp. In addition, FIG. 8D shows an equivalent circuit which includes drivers 30, 39 and receivers 32, 38 for providing bidirectional signal lines.
In a parallel interface using the circuits shown in FIGS. 8A and 8B, a host system can detect a status signal at a high level through the status signal line when the power of the interface device at the MFP side is turned off. However, in the case of FIG. 8C, the host system cannot judge die level of the status signal since the signal level of the status signal unstably varies according to the values of the pull-up resistors RP provided on the driver side 41 and receiver side 42.
FIG. 9 illustrates an interface arrangement for interfacing between an MFP and a host system, for example. The MFP receives command signals from the host and sends status signals to the host. Bidirectional data is also exchanged between the MFP and the host. However, since the protection diodes 34 for protecting against voltage leakage are generally used in common for all the pins of the interface, as illustrated in FIG. 9, the signal level of the status signal lines unstably varies according to the statuses of other signals from the host system when the MFP is in an energy savings mode. Accordingly, the host system cannot judge the level of the status signal lines. It may be possible for the host system to determine that the MFP is not in a usual machine idling mode (e.g., is in an energy savings mode), by detecting such an unstable status signal level from the MFP in response to a command signal from a host system. However, this signal handling would be nothing but a waste of performance for other operations which may be AL o being performed in the host system. Further, when an MFP having an energy saving function such as a power shut-down in a machine idling mode is connected to a host system, it may cause the drivers of the host system which do not conform to the energy saving function to erroneously operate.
Therefore, there is presently no interfacing apparatus available which is capable of appropriately notifying a host system of machine statuses.